Members of the group have been meeting with key lawmakers, testifying at legislative hearings, and circulating an online petition advocating against a bill that would lift a state-imposed cap on charter school enrollment. As of Sunday, the petition had received more than 2,200 signatures.

The campaign is believed to be the largest and most aggressive parent-driven effort in the state to stop raising the charter-school cap. It follows a similar effort by teachers unions, which have launched letter-writing campaigns to persuade legislators to oppose the measure.

Charter school advocates also have been lobbying legislators and have taken out ads on MBTA buses in support of more charter schools. Efforts on all fronts have been so intense that the Joint Education Committee decided last week to delay a decision on the legislation until this Tuesday.

“I have no problem with charter schools existing; it’s the way the state has decided to fund them,” said Heshan Berents-Weeramuni, cochairman of the school site council at the Curley K-8 School in Jamaica Plain and a member of Quality Education for Every Student, a grass-roots parent organization heading the effort. “It’s unfair.”

Controversy has long surrounded the funding of charter schools, public institutions that typically operate independently of local districts and rarely employ unionized teachers.

Under state law, every time a student enrolls in a charter school, thousands of dollars in state aid is diverted from his or her hometown district to cover their educational costs. In Boston, the school system is losing $87.5 million in state aid to about two dozen charter schools this year, even after factoring in several million dollars the city recieves in state reimbursement for charter-school tuition.

The amount of money Boston has been losing to charter schools has grown rapidly since 2010, when the state enacted a law that essentially enables the doubling of charter school enrollment in the city. Many charter schools are still creating the capacity to enroll all of those students, even as they lobby the Legislature for more seats.

The funding loss has been exacerbated in Boston for a variety of reasons that go well beyond the charter schools.

Most notably, school district officials overprojected enrollments for this year by hundreds of students, causing the district to open dozens of unneeded classrooms. Now, the district is readjusting enrollment figures for next year, which is leading it to cut per-pupil funding allocations to schools that had lower-than-expected enrollment this year.

Costs of running the 57,000-student system also are rising at a fast clip that cannot be covered by a nearly 4 percent proposed spending increase in the school system’s budget for next year.

All of that is causing dozens of schools to cut their budgets for next year, losing music programs, teacher aides, social workers, and other items.

“It’s too soon to raise the cap again,” said Megan Wolf, a Boston Latin School parent and Quest member. “We need to be working on improving the Boston public schools.”

Marc Kenen, executive director of the Massachusetts Charter Public School Association, said parents are wrongfully blaming charter schools for the Boston school system’s financial issues.

“Charter schools are not the cause of the budget problems facing the Boston public schools right now,” Kenen said.

Parents also have questioned the wisdom of expanding charter schools because they typically enroll fewer students with disabilities or those who lack fluency in English than the city’s school system.

“Siphoning money away from BPS toward charters hurts the most vulnerable: ELL students and students with disabilities. Where will they go?” Ellen Shattuck Pierce, whose children attend the Mendell School in Roxbury, said in an e-mail.

Kenen said charter schools have been increasing enrollment of those students, but he added more work remains.

Senator Sonia Chang-Diaz, a Boston Democrat and chairwoman of the joint committee, has been at the center of the debate. The former teacher resides in Jamaica Plain, where opposition to the charter-school cap lift runs high. But her district also includes other areas, such as Roxbury, where many families embrace charter schools.

Charter school advocates have criticized Chang-Diaz for holding up the bill, while opponents have applauded her for carefully considering the issue and raising concerns about the financial implications of more charter schools.

“If the charter cap gets lifted, it will lead to more budget cuts for every public school,” Berents-Weeramuni said. “It’s a very simple logical train wreck we see.”

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